Abstract: OBJECTIVE: To evaluate safety of MCPA-isooctyl and fluroxypyr-meptyl based on their digestion trends and residual levels on wheat. METHODS: The residue dynamics and final residue levels of 48% MCPA-isooctyl · fluroxypyr-meptyl · sulfentrazone suspension concentrates on wheat were carried out in three places for two years. The investigation involving three groups:wheat grain, plant and soil, and the digestion dynamics of MCPA-isooctyl and fluroxypyr-meptyl, were detected using high performance liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry. The three sets of samples were extracted with acetonitrile, the supernatant was purified by dispersive solid phase extraction, passed through the membrane,detected by gas chromatography-mass spectrometry and high-performance liquid chromatographytandem mass spectrometry,and also quantified by external standard method. RESULTS: The MCPA-isooctyl in wheat,plants and soil microorganisms was in the range of 0.005-0.2 mg/kg,and the fluroxypyr-meptyl in the range of 0.02-0.2 mg/kg. They showed a linear relationship with 0.05,0.1,0.2 mg/kg at 3 addition levels. The recovery rates were 77.0%-112.0%,the relative standard deviations were 1.1%-9.9%,and the limit of quantitative detection (LOQ) was 0.05 mg/kg. In 2 years (2016-2017) and in 3 places (Beijing, Henan, Ningxia), the digestion dynamic investigations show that the digestion half-life t_1/2 of fluroxypyr-meptyl on wheat plants in Beijing in 2016 was 5.92 d. In the soil samples in Beijing (2016) and Ningxia (2017),t_1/2 were 1.56 and 9.63 d,respectively. For comparison,the final residues of MCPA-isooctyl in wheat which were harvested at other times and other locations were <0.05 mg/kg. The final residues of fluroxypyr-meptyl were < 0.05 mg/kg which were lower than the national maximum residue limits for these two pesticides in wheat. CONCLUSION: MCPA-isooctyl and fluroxypyr-meptyl in winter wheat and soil had faster digestion rates. Therefore, 48% MCPA-isooctyl · fluroxypyr-meptyl · difluoro sulfentrazone suspension at the recommended dosage of 432 ga.i./hm² would probably not cause residual contamination of wheat and soil.

Key words: MCPA-isooctyl, fluroxypyr-meptyl, gas chromatography-mass spectrometry, high performance liquid chromatography-tandem mass spectrometry, wheat